Fusobacterium varium in cattle: prevalence and concentrations in healthy livers, liver abscesses, and ruminal and colonic epithelial tissues.

Fusobacterium varium has recently been revealed as the predominant Fusobacterium species in the bovine rumen. The species is a known pathogen and has been implicated in a wide range of infections in animals and humans. A preliminary study on F. varium in liver abscesses and gut epithelial tissues suggested that further investigation was needed to assess its potential involvement in liver abscesses. Thus, the objective of this study was to investigate the effects of in-feed tylosin or yeast plus clinoptilolite zeolite in beef-on-dairy heifers, dietary (low vs. high starch) and management strategies (regular vs. erratic feeding) in feedlot steers, and experimentally induced acidosis in steers on the prevalence and concentrations of F. varium in liver abscesses, liver scars, healthy livers, and ruminal and colonic tissues. Prevalence of F. varium was determined, before and after enrichment, by culture- and real-time, quantitative PCR (qPCR)-based methods. The culture method yielded F. varium isolates, generally after enrichment, from liver abscesses, liver scars and healthy liver tissues, however, qPCR liver samples were positive only after enrichment, suggesting a prevalence at low concentrations. Tylosin or yeast plus zeolite inclusion reduced prevalence of F. varium in healthy liver tissues, but not in liver abscesses. Dietary starch concentration and feeding practices did not affect prevalence in liver abscesses, liver scars, or ruminal or colonic epithelial tissues. Among the sample types analyzed, ruminal epithelial tissues had high prevalence (70 to 100%) and in quantifiable concentrations, however, concentrations were not affected by any of the treatments. Prevalence of F. varium in colonic epithelial tissues were lower than that of the ruminal epithelium and, generally, concentrations were below the detection limit. Induced ruminal acidosis did not affect prevalence in liver, ruminal or colonic tissues. These findings highlight the wide variations in F. varium prevalence in liver and gut tissues of feedlot cattle. Although F. varium was prevalent in liver abscesses, the low concentrations, expressed via the need for enrichment for isolation or detection, suggest that it is not likely contributing to liver abscess development. However, the high prevalence and concentrations in ruminal and colonic epithelial tissues indicate that F. varium is an active tissue invader and can contribute to ruminitis and colitis in cattle.